1. Field of the Invention
Example embodiments of the present invention relate to methods for transmitting data in wireless communication systems.
2. Description of the Related Art
FIG. 1 illustrates an example of a beamformed sector (or coverage area) provided by an access network 100 in a conventional wireless communications system. The conventional wireless communications system may be, for example, a code division multiple access (CDMA) system. As discussed herein, an access network may collectively denote one or more base stations and/or a radio network controller (RNC). As shown, one sector of the access network may include a number of antennas. In FIG. 1, three antennas 102, 104 and 106 are shown for example purposes. The antennas 102, 104 and 106 produce respective directional beams along respective directions 110, 112 and 114. The beam along direction 110 from antenna 102 has a coverage envelope or coverage area 118, the beam along direction 112 has a coverage envelope 120 and the beam along direction 114 has a coverage envelope 122. Hereinafter, the beam will be referenced by their respective direction; namely, in most instances, the beam will be referenced as beam 110, beam 112 and beam 114.
As illustrated in FIG. 1, the access network 100 may communicate with one or more access terminals 124, 126, 128, and 130 in a forward link by transmitting messages in a forward link channel and in a reverse link by transmitting messages in a reverse link channel. An access terminal may denote an individual user terminal, mobile station, etc. As discussed herein the forward link refers to a downlink transmission from the access network 100 to access terminals 124, 126, 128, and 130, and a reverse link refers to an uplink transmission from access terminals 124, 126, 128, and 130 to the access network 100.
As shown in FIG. 1, access terminals 128 and 130 are located in coverage envelope 118, and may communicate with the access network 100 in forward and reverse link channels allocated in beam 110. Access terminal 126 is located in coverage envelope 120, and may communicate with the access network 100 in the forward link and reverse link channels allocated in beam 112. Access terminal 124 is located in coverage envelope 122, and may communicate with the access network 100 in the forward link and reverse link channels over beam 114.
A forward link channel in each of the beams 110, 112, and 114 includes a forward pilot, a forward medium access control channel and one of a forward traffic channel or a forward control channel. The forward pilot, the medium access control channel, and traffic or control channel may be time-division multiplexed into time slots of length 2048 chips (1.66 . . . ms), and transmitted to access terminals 124, 126, 128, and 130 at the same power level. Each slot may be further divided into two half slots, each of which contains a forward pilot located at the midpoint of the half slot.
FIG. 2 illustrates example half slots 510, 520, and 530, which may be transmitted over beams 110, 112, and 114, respectively. As shown in FIG. 2, each of the half slots 510, 520, and 530 include the same forward pilot 512 time multiplexed with data transmitted over the forward medium access control MAC and forward data traffic channel DATA.
In conventional wireless communications systems, the forward pilot 512 may identify the serving access network 100 (i.e., the source of transmission) to the access terminals 124, 126, 128, and 130, and may be used in determining a maximum forward link data rate by measuring a signal-to-interference and noise ratio (SINR) of the forward pilot 512. The maximum forward link data rate may represent a forward link data rate at or below which data may be transmitted.
For example, each access terminal 124, 126, 128, and 130 may measure a signal-to-interference and noise ratio of (SINR) the forward pilot 512 transmitted sector wide, or in other words, to each of the access terminals 124, 126, 128, and 130. Each access terminal 124, 126, 128, and 130 may then use the measured SINR to predict a carrier-to-interference C/I ratio of a next transmission in each access terminal's respective forward link channel. The predicted C/I may then be used in determining a maximum forward link data rate.
Referring again to the sector of FIG. 1, each access terminal 124, 126, and 128 may predict a C/I ratio and subsequently a maximum forward link data rate based on the same forward pilot 512. However, each of the beams 110, 112, and 114 may have distinct channel characteristics (e.g., C/I ratios), and thus may be capable of a higher maximum forward link data rate than estimated based on the SINR of the forward pilot 512.